Protective device



Dec. 22, 1953 A. T. sTRATToN 2,663,776

PROTECTIVE DEVICE Filed Aug. 18, 1949 lplfthur T. Stratton. www Q A NM Patented Dec. 22, 1953 PROTECTIVE DEVICE Arthur T. Stratton, Murrysville, Pa., assigner to Westinghouse Electric Corporation,A East Pittsburgh, Pa., aA corporation of Pennsylvania` Application August 18, 1949, Serial No. 110,964

17 Claims.

This invention relates to protective devices for electric circuits and more particularly to an electric circuit breaker of the fuseless cutout type.

Fuseless cutout devices have heretofore been proposed for use in the protection of high ten sion electric circuits, and it has been determined that their use avoids many of the disadvantages and cliniculties inherent in cutouts of the type employing replaceable fuses. The main advantage of course is the elimination of the necessity of fuse replacement when the fuseless cutout operates to automatically interrupt the circuit upon the occurrence of any overload condition. In. all of the prior fuseless cutouts however, a rather complicated arrangement of parts is utilizccl which renders the devices expensive to manufacture, install and maintain in a proper condition of adjustment and repair.

it is accordingly an object of the present invention to provide a protective device of the fuseless cutout type which comprises relatively few parts and which so constituted as to overcome the objections and disadvantages of the prior cutouts.

Another object is to provide a novel fuseless cutout for the protection of electric circuits, which is of relatively simple construction and which is compact, rugged and thoroughly reliable in operation.

A further object is to provide in a. protective device oi the abovel character a novel construction which materially simplifies the resetting of the contacts following a separation thereof due to an overload condition.

A. still further object resides in the provision of a novel arrangement of partsv for a protective device of the above character, which includes a housing provided. with a pivoted closure member, the construction being such that a manual open.- ing and reclosing oi' the circuit may be accom- Dlshed solely by pivotal opening movement of the closure member.,

Other objects and novel features of the'invention will appear more fully hereinafter from. a consideration of the following detailed description when taken in connection with the accompanying drawing. It is to be expressly understood however, that the drawing is utilized for purposes of' illustration only and is not to be taken. as a definition of thev limits oi the, invention, reference being had for this purpose to the appended claims.

In the drawing whereinsimilar reference characters refer to similar parts throughout the sev-eral views:

Fig. l is a Vertical sectional view of a protective device constructed in accordance with the present invention, the same illustrating the parts in normal circuit-closing position;

Fig. 2 is a view similar to Fig, l but showing lthe position of the parts following the automatic separation of the contacts in accordance with an abnormal load condition;

Fig. 3 is a view similar to Fig. 1 and showing the manner in which the contacts are reclosed and latched, and

Fig. 4 is a sectional view taken substantially along line IV-IV of Fig. 1, the linkage between the door and interruptor tube having been omitted in order to more clearly illustrate the pivotal mountings for the interruptor tube and door.

Referring more particularly to Fig. l of the drawing, a protective device of the fus-eless cutout .type embodying the principles of the present invention is illustrated therein as comprising a housing i0 of porcelain or similar insulating material, provided with an integrally formed gas barrier l2 disposed between stationary line terminals I4 and t6. As shown, the housing l0 is provided with an open side which is normally closed by a door i8 of insulation material, the latter being pivotally mounted in the housing as by means of a pair of arms 28 and 22 which are connected to hinge pins 24 and 26 supported by the sides of the housing adjacent the bottom thereof, see Figs. 3 and 4. The door I8 is preferably provided with an integral eyelet handle 28 which may be manually grasped or which may receive the hooked end of a switch stick in order to open the door and actuate the interruptor contacts within the housing in a manner which will appear more fully hereinafter.

A novel interruptor mechanism is positioned within the housing I and includes an interruptor 3u comprising a lower tube 32 and an upper guide member 34, both of these parts being constructed of insulating material and being connected together by a threaded collar 35. At its lower end, the` tube 32v threadedly receives a terminal ferrule 3l provided with an extension 33 for engagement with a stationary contact 40 of the terminal l5.. Asr illustrated, the ferrule 31 and hence the interrupter 30, is pivotally mounted on the same axis as the door1 I8, this arrangement being achieved in any suitable manner as by pivot pins 24 and 26 being secured to ferrule 3l. DueA to this construction and in accordance with certain phases of the operation of the device, the door |38 and ther nterrupter 3D- may be both pivotally moved about the pins 24 and 26.

separable contact means. are provided within the interruptor for interrupting a, 1aed Circuit associated with the protective device, and in the forro oi the invention illfstrated, such means includes rod which is provided at its lower end with split contact .ring 33 for engagement with the ferrule in the closed circuit position illustrated in Fig. l. Also secured to the lower end of the rod l2 is a follower lil of insulating material which normally projects downwardly and serves as a reliable indicator of the condition or" the device. At its upper end, the rod 42 is guided for reciprocable movement by the guide member 3e, the construction including a head it provided with a plurality of extensions i8 which in turn are received in and guided by vertically arranged slots 5t provided in the wall of the guide ineniber 3e.

Novel means are provided for normally maintaining the separable contacts, constituted by the ring #i3 and the errule 3l, in engagement while allowing prompt disengagement thereof in response to a normal operation or an overload condition. In the form shown such means includes a latch lever 52 which is pivoted to the collar at 55s and is normally urged to the latching position illustrated in Fig. 1 by means of a spring 56. In this position, a notch 53 on the latch lever 52 engages one of the extensions 138 of the head llt and serves to maintain a spring 5S in a compressed condition. Such spring 53 is interposed between the extensions and the collar 3E and constantly tends to inove the head it and rod upwardly with respect to the tube 32 to separate the contacts stl' in the manner illustrated in Fig. 2. When the head i5 is latched, as shown in Fig. l, the latch lever extends substantially vertically upward and is provided with an inclined end surface et in engagement with the free end of a biinetal strip 52. Such free end is electrically connected with the head fcthrough a flexible conductor with the other end of the bimetal being secured to a contact block i323 carried by the door IS. lirnetal strip E2 is formed in a well known manner of a pair of laminations of materials having diiierent coenicients of expansion internally secured together with the lamination having the greater coefficient of expansion being located uppermost. rhe circuit from the bimetal to the line terminal contact Ill is completed by way ci a contact spring latch 68, the free end of which is received within a notch on top of the block It will thus be perceived that the latch @t serves te releasably latch the door l 8 in its closed position, while the said latch together with the blocl E5 constitute disconnecting contacts which separate when the door I8 is opened.

The interruptor ed is maintained in the position shown in Fig. l by a U-shaped spring clip TS which is secured to the casing in any suitable manner, such as to terininal ill and is provided with sprin Cr arrns for embracing opposite sides of a top cap "l2, threadedly received by the upper end or" guide member tl. A similar retaining spring clip it is secured to the door i8 and is adapted to releasably hold the door and interrupter in assembled relation when these parts are removed from the housing it.

In addition to the foregoing features of construction, the present invention provides a novel arrangement for normallv separating the contacts lil, and for reclosing the said contacts in the event they have been manually or automatically separated. More particularly and referring to Fig. 1, such construction includes two pairs of pivotally connected links disposed on each side oi the interruptor 3Q, each pair including a link 'le pivoted to the head it at it, and a link 83 pivoted to the door i8 at S2, the two links being pivoted together` at @il as illustrated. In addition to the linl; arrangement, a resilient retaining iinger secured to the line terminal it and provided with a cent end portion i3d is provided for releasing latch lever 52 to allow separation of the contacts 3l, t3, all in a manner which will appear more fully hereinafter.

With the parts in the closed circuit position shown in Fig. 1, the circuit through the novel protective device may be traced from the upper line terminal lli, through the contact latch te to block t on door i3, through binietal strip and thence to the lower line terminal it by way of the flexible conductor Eli, head t, rod :i2 and the closed contacts 3l, Under these conditions the follower lli will project below the housing i il and thus indicate the closed circuit condition oi the device. When overload occurs in the circuit with. which the protective device is associated, the binietal will be heated thereby and the free end will deflect downwardly in engagement with the inclined surface 5@ of the upper end or the latch lever to move the latter to the unlatched position shown in Fig. 2 where the notch 58 is moved out of engagement with the head The expansible spring 5t will then rapidly lnove the rod l2 upwardly and quickly separate the contacts 3l and Such separation of the contacts will draw an are which will be restricted by the follower la in the relatively small annular space between the follower and the interrupter 'tube 32. Preferably, tube i2 and iollower il are of an insulating material such as ber which is capable ci evolving an arcextinguishing gas when in proxin ity to an electric arc in order to more quickly quench the arc which accompanies the separation of the oontacts El and t3. When the circuit opens, as thus described, the follower is drawn up into the housing iii, thereby clearly indicating at the eXterior that the circuit of the device is open.

To eiiect reclosure of the contacts 3l, it is only necessary to pivotally inove the door i3 to the open position illustrated in Fig. 3. Such opening of the door inay be effected inserting the end. of a Switch stick within the eyelet 0f the handle 253. As the door is opened, the interrupter Bil is maintained in the position shown by the relatively strong retaining clip lil, while the friction clip lll between the door and the tube 32 which is relatively weak readily releases friotional engagement with the interrupter tube 32. Separation of the contacts t and @8 will not then draw any arc in view ci the fact that the circuit is then open through the interruptel el?. It will be readily understood that as the door is pivotally moved from the closed position shown in Fig. 2 to the open position shown in Fig. 3, the link connection between the head it and the door it, comprising pivotally connected links 'I6 and 8B, will move the rod .li-2 and the contact 55 downwardly in order to compress the spring 53 and reclose the contacts 3l and llt. During this operation, the latch lever will be reset by spring 5t urging the latch bar to reengage its notch 5S with the head lo as soon as the latter moves downwardly past the notch. It will thus be Seen that due to the novel features provided, a simple, pivotal opening movement of the door i8 a predetermined amount, will reclose the interruptor contacts e3, 3l, compress the spring 5t, and reset the latch 52,

Following the reclosure of the separable contacts llt, 3l', as above described, the circuit may be restored by merely pivotally moving the door to the closed position shown in Fig, 1. When the door is closed, the circuit is completed through the contacts t6 and 68, the bimetal 62 in the meantime having cooled down to be denected back to its original position.

If it is desired to inspect or service the device, the door may be pivotally opened to an extent greater than that illustrated in Fig. 3. Under` these conditions, the links 16 and 80 will move the interruptor 39 about its pivotal mounting 24, 25 and release the same from frictional engagement with the spring clip 1t. The door and interruptor may then be pivotally moved to a -depending position with respect to the housing lo and removed entirelyr from the housing, if desired. This may be accomplished by slots l5 provided in opposite side Walls of housing I0 through which pivot pins 24 and 2li may be removed. In reassembling the interruptor and door with the housing, he interrupter is so placed with respect to the door as to be engaged by the spring clip lil. The assembly of the interruptor and door is then pivotally attached to housing lll and pivotally moved to the closed circuit position in the manner heretofore described.

In addition to the foregoing features, the invention provides a novel arrangement whereby the circuit may be manually opened by merely pivotally opening the door a slight amount. Thus it will be observed from Fig. l that with the latch lever 52 set in latched position, and the links 'i6 and 89 folded as shown, the interruptor is releasably held to the door I8 by these links and friction clip 74. Hence as `the door initially opened, the interruptor 3B will be pivotally moved with the door an amount suilicient to cause the end portion 88 of the retaining finger 86 to hold the latch lever 52 until the head c has cleared the notch 58, even though friction clip 14 is not strong enough to pull the interrupter completely out or retaining clip 1D. The contacts 3l, 45 Will thereupon be immediatelyv separated as heretofore described, and this action taires place before the contacts 66 and 5S are separated. Hence the arc will occur within the interruptor tube 32 and will be drawn out and extinguished in the manner previously pointed out. It is understood that further opening movement of the door to the position shown in Fig. 3 wili first separate disconnecting contacts d and ES, and then reclose the contacts 3l, 43, compress the spring 5S and reset the latch lever 52, it being pointed out that the spring clip lil holds the interruptor' Within the housing during such further opening' movement of the door.

There has thus been provided by the present invention, a novel protective device of the fuseless cutout type which embodies a relatively simple construction but which is highly eiclent in its operation. The number of constituent parts of the device has been reduced to a minimum and hence the same may be manufactured and maintained` in proper working condition at a relatively lovv cost. Manual opening and reclosing of the separable contacts may be accomplished by a single pivotal opening movement of the door, thus avoiding the complicated constructions and the accompanying diculties of the` devices previously proposed. In addition to the foregoing and other advantages, the use of the follower 44 provides in addition to its arc eX- tinguishing function, a readily visible indication o1 the condition of the circuit of the protective device.

While the invention has been illustrated and described herein with considerable particularity, it will be readily understood by those skilled in the art that various modications may be resorted to without departing from the spirit of the invention. Reference will therefore be had to the appended claims for a definition o the limits of the invention.

I claim as my invention:

l. In an electric protective device, a housing with open side, a door of suitable rigid material for closing said open side, a circult interruptor mounted in the housing and including a pair ot separable contacts, means pivotally mounting said door l.For movement relative to said housing and said circrit interrupter, means in said housing responsive to a predetermined conditi-on oi the t eating separation of said contacts to inte associated with said interrup is closed, and, a lost motion connection between eration but responsive to pivotal opening movement of the door with respect to the housing and interruptor for reclosine said contacts.

2. In an electric protective device, a housing provided with an open side, a door of suitable rigid material for closing said open side, a circuit interrupter mounted in the housing and including a pair or" relatively7 movable parts which are biased apart, a contact connected with each of said parts, means pivotally mounting said door for movement relative to said housing and said circuit interruptor, latch means for normally maintaining said parts and contacts in a circuit closing position, means including electro-responsive means for releasing said latch means to separate the contacts and interrupt a load circuit associated with said interrupter in response to an overload condition, and a lost motion connection between one of said parts and said door permiti ting separation of said contacts without movement of said door but operable upon pivotal opening movement of the door with respect to the housing and interrupter for moving said one part to reclose said contacts.

3. In an electric protective device, a housing 'provided With an open side, a door of suitable rigid material for closing said open side, a circuit interrupter mounted in the housing and including a pair of separable contacts, means pi"- otally mounting said door for movement relative to said housing and said circuit interruptor, means for effecting separation of said contacts to interrupt a load circuit associated with said interruptor, and pivoted links interconnecting one of said contacts and the door and occupying a folded position when said door contacts are closed t0 be straightened out upon separation movement of said contacts relative to said door to form a drive connection between the door and said one contact eiective in response to pivotal opening movement of the door ufitl'i respect to the housing yand interruptor for closing the contacts.

4. In an electric protective device, a housing provided with an open side and bottom, door of suitable rigid material for closing open side, means for inovably connecting door to the housing, a circuit intv mounted in the housing and including an rrupter tube provided with a xed Contact, said interruptor 'accento 7 tube extending generally vertically in said housing with its lower end being open and located near the open bottom part of said housing and its fixed contact located adjacent the lower end of the tube, said interruptor including also a movable element in said tube carrying a movable contact and a follower element below the movable contact which normally extends out through the lower end of the tube and housing when the contacts are in engagement to be visible from the exterior, said movable element being biased upwardly, to separate said contacts, a latch normally operative to maintain said movable element in a position to close the contacts, means responsive to an overload condition for releasing said latch to allow movement of said element under the inuence or" the resilient means to separate the contacts and interrupt a load circuit associated with the interrupter and to withdraw said follower element into said tube and housing.

5. In an electric protective device, a housing provided with an open side, a door of Suitable rigid material for closing said open side, means for pivotally connecting said door to the housing, a circuit interrupter within the housing and including an interruptor tube provided with a fixed Contact and including also a movable element carrying a movable contact, eX- pansive resilient means constantly tending to separate said contacts, a latch normally operative to maintain said movable element in a position to close the contacts and compress said resilient means, means responsive to an overload condition for releasing said latch to allow movement or said element under the influence of the resilient means to separate the contacts and interrupt a load circuit associated with the interrupter, and a pair of pivotally connected links interconnecting the door and said movable element for moving the latter to a position to reclose the contacts, compress said resilient means and reset the latch, upon opening movement of the door.

6. In an electric protective device, a housing provided with an open side, a door of suitable rigid material for closing said open side, means for pivotally connecting said door to the housing, a circuit interrupter within the housing and including an interruptor tube provided with a ilxed contact and including also a movable element carrying a movable contact, expansive resilient means interposed between the tube and the movable element constantly tending te move the latter in direction to separate said contacts, a latch engageabie with the movable element to normally maintain the latter in a position to compress said resilient means and close the contacts, bimetallic means responsive to an overload condition to release the latch to allow movement or" said element under the innuence of the resilient means to separate the contacts and interrupt a load circuit associated with the interrupter, and a pair of pivotally connected links interconnecting the door and said movable element for moving the latter to a position to reclose the contacts, compress said resilient means and reset the latch, upon opening movement of the door.

'7. In an e ectric protective device, a housing provided with an open side, a door of insulation material for closing said open side, a circuit interrupter mounted in the housing and including a pair of separable contacts, means pivotally mounting said door for movement relative to said housing and said circuit interrupter, a pair of disconnecting contacts arranged in series with said separable contacts, one of said disconnecting contacts being carried by said door and the other carried by the housing, means responsive to pivotal opening movement of the door a predetermined amount for sequentially eiecting separation of said separable contacts and said disconnecting contacts, and lost motion connection between said door and the movable one of said separable contacts permitting separation of said contacts without movement of said door but responsive to pivotal opening movement of the door beyond said predetermined amount for reclosing said separable contacts.

8. In an electric protective device, a housing provided with an open side, a door of suitable rigid material for closing said open side, a circuit interrupter within the housing and including a pair oi-` separable contacts, means pivotally mounting said door for movement relative to said housing and said circuit interrupter, means responsive to initial pivotal opening movement of the door with respect to the housing for effecting separation of said contacts, and lost motion connection between said door and the movable one of said separable contacts permitting separation of said contacts without movement of said door but responsive to continued pivotal opening movement of the door with respect to the housing for reclosing said contacts.

9. In an electric protective device, a housing provided with an open side, a door of suitable rigid material for closing said open side, means for pivotally connecting said door to the housing, a circuit interrupter within the housing and including a pair of separable contacts, means for pivotally mounting said interruptor in said housing, means operated by initial pivotal opening movement of the door with respect to the housing for moving said interruptor about its pivotal mounting, means operable in response to such initial pivotal opening movement of the interrupter to eiect separation of said contacts, means permittng further pivotal movement of the door without further pivotal movement of the interrupter after separation of said contacts, and means dependent upon continued pivotal opening movement of said door with respect to the housing for reclosing said contacts.

10. In an electric protective device, a housing provided with an open side, a door of suitable rigid material for closing said open side, means for pivotally connecting said door to the housing, a circuit interrupter within the housing and including a pair of separable contacts, an expansive spring constantly tending to separate said contacts, latch means for normally maintaining said spring in a compressed condition with said contacts closed, means for pivotally mounting said interruptor in said housing, means operated by initial pivotal opening movement of the door with respect to the housing for moving said interrupter about its pivotal mounting, means operable in response to such initial pivotal opening movement of the interrupter to trip the latch means to allow the spring to expand and separate the contacts to interrupt a load circuit associated with said interruptor, means permitting further pivotal movement of the door without further pivotal movement of the interrupter after separation or said contacts, and means dependent upon continued pivotal opening movement of said door with respect to the housing for reclosing the contacts, compressing said spring and resetting the latch means.

11. In an electric protective device, a housing provided with an open side and having spaced line contacts therein, a door of suitable rigid material for closing said open side, means for pivotally connecting said door to the housing, a circuit interrupter within t e housing and having spaced terminals and a pair oi separable contacts connected in series therewith, means for pivotally mounting said interrupter within the housing for movement of one terminal thereof into and out ci engagement with a line contact, means responsive to initial pivotal opening movement of the door with resp-ect to the housing for effecting separation oi said contacts, means responsive to further pivotal opening movement of the door for reclosing said contacts, releasable means in housing engaging said interrupter for holdingl said one interrupter terminal and its contact in engagement during the aforesaid opening and reclosing -oi said contacts and means responsive to a still further pivotal opening movement of the door for releasing said holding means and moving said interrupter about its pivotal mountingr to expose the same for inspection or repair.

12. In an electric protective device, a housing provided with an open side, a door of suitable rigid material for closing said open side, means for pivotally connecting said door to the housing, a circuit interrupter within the housing and including a pair of separable contacts, means for pivotally mounting said interrupter in the housing, and means responsive to continued pivotal opening movement or the door with respect to the housing for sequentially iirst effecting separation of said contacts, thereafter effecting reclosure oi said contacts, and iinally moving the interrupter with the door to at least partially remove the interrupter from the housingr for inspection and repair.

13. A circuit interrupter comprising, an opensided housing, a door oi suitable rigid material mounted on said housing for movement between open and closed positions relative to the open side of the housing, a circuit interrupter mounted on said housing for movement into and out of said housing, spaced line contacts in said housing, terminals on said interrupter adapted to engage said line contacts when said interrupter is within said housing, and at least one or said terminals moving out of engagement with its line contact when said interrupter is moved out of said housing, means for normally holding said interrupter in said housing, said interrupter having separable contacts in series circuit relation with the interrupter terminals, means responsive to a predetermined condition of the circuit for causing separation oi said interrupter contacts, a lost motion connection between said door and a movable interrupter contact permitting separation of said interrupter contacts Without movement of said door from its closed position while said lost motion is taken up, whereby opening movement of said door following separation of said interruptor contacts closes said interrupter contacts, and said door can be then closed without causing movement of said interrupter or operation of the interrupter contacts.

14. A circuit interrupter comprising, an opensided housing, a door of suitable rigid material mounted on said housing for movement between open and closed positions relative to the open side of the housing, a circuit interrupter mounted on said housing for movement into and out of said housing, spaced line contacts in said i sive tca predetermined con 10 housing, terminals on said interrupter adapted to engage said line contacts when said interrupter is within said housing, and at t ci e of said terminals moving out or engagern .fith its line contact when said interrupt1 i oved out of said housing, means `for norma.- ing said interrupter in said housing, said ter having separable contacts in series circuit relation vwith the interrupter terminals, inea-ns respon- E he circuit for causing' separation of said interi pter contacts, a lost motion connection `between said door and a movable interrupter contact permitting separation of interrupter contacts without movement of said door from closed position while said lost motion is taken up, whereby opening nio-vement oi said door folicwing separation of said interruptor contacts clases said interrupter contacts, and said door can be then closed without causing movement of said interrupter or operation of the interrupter contacts, and means on said door for causing separation oi said interrupter contacts in response to initial opening movement of said door.

15. A circuit interrupter comprising, an opensided housing, a door of suitable rigi material mounted on said housing for movement between open and closed positions relative to the open side of the housing, a circuit interrupter mounted on said housing for movement i 'o and out of said housing, spaced line contacts in said housterminals on said int rrupter adapted to engage said line contacts when said interrupter is within said housing, and at ieast one of said terminals moving out of engagement with its line Contact when said interrupter is moved out of said housing, releasable means for normally holding said interrupter in said housing, said interrupt-er having separable contacts in series circuit 'i f relation with the interrupter terminals, means responsive to a predetermined condition of the circuit ior causing separation of said interrupter contacts, a lest motion connection between said door and a movable interrupter contact permitting separation of said interrupter contacts without movement or" said door from its closed position while said lost motion is taken up, whereby opening movement of said door following separation of said interrupter contacts closes, intcrrupter contacts and said door can be thus closed without causing movement of said interrupter or operation oi the interrupter contacts, and a stop for said interrupter contacts when closed so that additional force may then be exerted on door in the opening direction to release said releasable means and move said interrupter out or said housing.

16. A circuit interrupter compr sided housing, a door or suitable pivotally mounted on said housing or movement between. open and closed posi:V ons relative to the open side of the housing, a circuit interrupter in said housingy said interrupter having separable contacts, means responsive to a predetermined condition of the circuit for causing separation or" said interrupter contacts, a lost inotion connection between said door and a movable interrupter contact permitting separation said interrupter contacts without movement of said door from its closed position while said lost inotion is taken up, whereby opening movement oi said door following separation of interrupter contacts clos-es said interrupter contacts and said door can be then closed without causing l movement of said interrupter or operation ofthe interrupter contacts.

17. A circuit interrupter comprising, an opensided housing, a door of suitable rigid material pivotally mounted on said housing for movement between open and closed positions relative to the open side of the housing, a circuit interrupter in said housing, said interrupter having separable contacts, means for normally holding said interrupter in said housing, said interrupter having separable contacts in series circuit relation with the interrupter terminals, means responsive to a predetermined condition of the circuit for causing separation of said interrupter contacts, a lost motion connection between said door and a movable interrupter contact permitting separation of said interrupter contacts without movement of said door from its closed position while said lost motion is taken up, whereby opening movement of said door following separation of said' interrupter contacts closes said interrupter contacts and said door .can be then closed without causing movement of said interrupter or other operation of the interrupter contacts, and means on said door for causing separation of said interrupter contacts in response to initial opening movement of said door.

ARTHUR T. STRATTON.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,973,378 Graesser Sept. 11, 1934 2,272,717 Ludwig Feb. 10, 1942 2,280,493 Kinney Apr. 21, 1942 2,301,746 Parker Nov. 10, 1942 2,357,853 Smith Sept. 12, 1944 2,424,126 Smith July 15, 1947 2,472,625 Smith July 7, 1949 

